Heater for fast warmup cathode

ABSTRACT

Heat loss from a fast warmup cathode heater is minimized by keeping the coiled body portion of the heater small in relation to the length of the heater legs and by increasing the thickness of the insulating coating on the legs by a factor of about 400% over that on the coils.

United States Patent 1 1 Buescher et al.

1451 May 13,1975

[ HEATER FOR FAST WARMUP CATHODE {75] Inventors: William E. Buescher;Donald R.

Kerstetter, both of Emporium, Pa.

[73] Assignee: GTE Sylvania Incorporated,

Stamford, Conn.

[22] Filed: Feb. 8, 1974 [21] Appl. No.: 440,684

2/1970 Katz 313/337 X l/197l Bakker et al. 313/337 PrimaryExaminerSaxfield Chatmon, Jr. Atrorney, Agent, or FirmNorman J. OMalley;William H. McNeil]; Cyril A. Krenzer [57] ABSTRACT Heat loss from a fastwarmup cathode heater is minimized by keeping the coiled body portion ofthe heater small in relation to the length of the heater legs and byincreasing the thickness of the insulating coating on the legs by afactor of about 400% over that on the coils.

2 Claims, 1 Drawing Figure PATENTED W I 31975 l a: .......m\.....

HEATER FOR FAST WARMUP CATHODE BACKGROUND OF THE INVENTION Thisinvention relates to heaters for fast warmup cathodes and moreparticularly to heaters for use in the cathodes of television picturetubes.

In the past many types of fast warmup cathodes have been proposed;however, most have not been commercially acceptable because of highfailure rates or prohibitive costs. To accomplish the same result manymanufacturers of television receivers have adopted a so-called instanton feature which provides heater current to all of the tubes in thereceiver even if it is of While this system is very successful inaccomplishing its purpose, it is very wasteful of electrical energy.

To rectify the energy waste, attention has again turned to providing afast warmup cathode; that is, a cathode which will reach operatingtemperature and provide a viewable picture on the screen of a cathoderay tube in the neighborhood of5 seconds. Such a cathode has recentlybeen developed and is shown and described in US. patent application Ser.No. 409,041, assigned to the assignee of the present invention, thedisclosure of which is herein incorporated by reference.

Such a cathode comprises basically a cup-shaped cap having electronemissive material on the closed end thereof and a cathode stack which isattached to the cap ,by low heat conducting ribbons. This structureworks extremely well for its designed purpose but could be improved evenfurther if heat loss could be minimized from the heater encompassedtherewithin.

OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, an object of thisinvention to obviate the disadvantage of the prior art.

It is another object of the invention to enhance heater operation infast warmup cathodes.

Still another object of the invention is the provision of a heater for afast warmup cathode which has minimized heat loss.

These objects are accomplished in one aspect of the invention by aheater which comprises an electrically conductive core substantiallycoveredby an electrically insulating material. The heater is formed toprovide a coiled body portion with a pair of extending legs. The heightof the coiled body portion is small compared to the legs and to minimizeheat loss from the legs the thickness of the insulating material thereonis substantially greater than that of the coiled body portion.

BRIEF DESCRIPTION OF THE DRAWINGS The single FIGURE is a cross-sectionalelevational view of a heater constructed in accordance with theinvention mounted within a suitable cathode.

DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding ofthe present invention together with other and further objects,advantages and capabilities thereof, reference is made to the followingdisclosure and appended claims in connection with the above-describeddrawing.

Referring now to the drawing with greater particularity there is shown afast warmup cathode 10 comprising a top cap 12 which is substantiallycup shaped and includes a closed end 14 having a peripheral'side wall 16defining a hollow interior 18.

Top cap 12 is supported by a plurality of minimum contact areas 20formed as part of a hollow cathode sleeve 22.

A heater 24 having an electrically conductive core 26 of a suitablematerial such as tungsten or molybdenum, surrounded by an electricallyinsulating coating 28, of a suitable material, such as alumina ispositioned within the cathode 10. The heater 24 is formed to provide acoiled body portion 30, which is of small height compared with theheight of the heater, which body portion is encompassed within thehollow interior 18 of top cap 12. A pair of legs 32 extend from body 30through sleeve 22. To minimize heat loss from the extended pair of legs32 the electrically insulating coating thereon is of much greaterthickness than the coating on coiled body portion 30. To be effectivethe leg coating should be at least 300% and preferably 400% thicker thanthat on body portion 30. The terminal ends of legs 32 are left bare ofinsulation so that electrical connection can be made thereto.

In actual tests a heater having a coiled body portion coating thicknessof 0.0017 inch and a leg coating thickness of 0.0068 inch showed a 5%improvement in warmup time compared with a heater having a uniformcoating of 0.0017 inch. Such a reduction is indeed significant in anarea where warmup time reduction is measured in hundredths of a second.

While there have been shown what are the preferred embodiments of theinvention, it will be apparent to those skilled in the art that variouschanges and modifications can be made herein without departing from thescope of invention as defined by the appended claims.

What is claimed is:

1. A heater for a fast warmup cathode comprising: a metallic,electrically conductive core; and an electrically insulating coatingsurrounding said core; said heater being formed to provide a coiled bodyhaving a pair of legs extending therefrom, the height of said coiledbody being small compared with the length of said legs; the insulatingcoating on said pair of legs having a thickness about 400% greater thanthe thickness of the insulating coating on the coils of said coiled bodyportion.

2. The heater of claim 1 wherein said insulating coating is alumina.

1. A heater for a fast warmup cathode comprising: a metallic,electrically conductive core; and an electrically insulating coatingsurrounding said core; said heater being formed to provide a coiled bodyhaving a pair of legs extending therefrom, the height of said coiledbody being small compared with the length of said legs; the insulatingcoating on said pair of legs having a thickness about 400% greater thanthe thickness of the insulating coating on the coils of said coiled bodyportion.
 2. The heater of claim 1 wherein said insulating coating isalumina.